Chapter 2 Database System Architecture Prof YinFu Huang

Chapter 2 Database System Architecture Prof. Yin-Fu Huang CSIE, NYUST

2. 1 Introduction n A framework: ANSI/SPARC study Group on Data Base Management Systems Advanced Database System 2

2. 2 The Three Levels of the Architecture n The three levels: (See Fig. 2. 1) a. The internal level b. The external level c. The conceptual level Advanced Database System 3

Example (Fig. 2. 2) Advanced Database System 4

The interrelationships (Fig. 2. 3) Advanced Database System 5

2. 3 The External Level n Data sublanguage vs. host language n Tightly coupled vs. loosely coupled n Data definition language (DDL) vs. Data manipulation language (DML) n External view, external record, and external schema Advanced Database System 6

2. 4 The Conceptual Level n Conceptual view, conceptual record, and conceptual schema. n A great many additional features, such as the security and integrity constraints. 2. 5 The Internal Level n Internal view, internal record, and internal schema n The internal view is still at one remove from the physical level. Advanced Database System 7

2. 6 Mappings n The conceptual/internal mapping n The external/conceptual mapping n The external/external mapping Advanced Database System 8

2. 7 The Database Administrator n The functions: a. defining the conceptual schema (logical database design) b. defining the internal schema (physical database design) c. liaising with users d. defining security and integrity constraints e. defining dump and reload policies f. monitoring performance and responding to changing requirements Advanced Database System 9

2. 8 The Database Management System n Procedures: a. A user issues an access request. b. The DBMS intercepts the request and analyze it. c. The DBMS inspects the external schema for that user, the external/conceptual mapping, the conceptual schema, the conceptual/internal mapping, and the storage structure definition. d. The DBMS executes the necessary operations on the stored database. Advanced Database System 10

The functions (Fig. 2. 4) a. Data definition b. Data manipulation n Planned requests vs. unplanned requests c. Optimization and execution d. Data security and integrity e. Data recovery and concurrency (transaction manager) f. Data dictionary g. Performance Advanced Database System 11

2. 9 Data Communications n The DC manager is not part of the DBMS but is an autonomous system in its own right. n Database/data-communications system Advanced Database System 12

2. 10 Client / Server Architecture n A server (the backend) and a set of clients (frontends) (See Fig. 2. 5) n Applications a. user-written applications b. vendor-provided applications (tools) n The possibility arises of running clients and servers on different machines. Advanced Database System 13

2. 11 Utilities n Utilities: a. Load routines b. Unload/reload routines c. Reorganization routines d. Statistical routines e. Analysis routines Advanced Database System 14

2. 12 Distributed Processing n The DBMS backend on one machine and the application frontends on another. (See Fig. 2. 6) n Many arguments in favor of such a scheme: a. parallel processing b. server ⇒ a database machine c. client ⇒ a personal workstation d. A single database might be shared across several distinct client systems. (See Fig. 2. 7) Advanced Database System 15

One server machine, many client machines (Fig. 2. 7) Advanced Database System 16

A distributed database system (Fig. 2. 8) Advanced Database System 17

2. 12 Distributed Processing (Cont. ) n User accesses can basically be provided in two different ways: a. A given client might be able to access any number of servers, but only one at a time. The user in such a system has to know which particular machine holds which pieces of data. b. The client might be able to access many servers simultaneously. The servers look to the client as if they were really a single server, and the user does not have to know which machines hold which pieces of data. Advanced Database System 18

The End. Advanced Database System 19